Help a newb tune his carbs

[mrkelvinator]

Hey Guys,

Firstly I'd like to that every one who has responded to my previous newb posts, it has been a real help

So I've got a 1979 XS650 (Special?) with Mikuni VM34 Carbs - i believe thats the only modification done to it. And here it is on charge

The problem:
Before i start messing around with the carbs (which have been cleaned). The bikes starts on choke with some throttle and revs if i continue to open the throttle. However without throttle it wont start or will die after starting. It will not start without choke - with or without throttle.
My guess is that its not getting enough fuel hence the choke and the idle needs to be adjusted...what do you guys think?
I have the manuals that have been suggested in other posts, but just wanna know what the problem is before making any changes.

The exhausts are stock, but I believe that the previous owner has drilled holes in them...the two yellow things are cork plugs, the hole on the top is without one. Is this normal??...

Thanks for all your help

And here are the carbs:

 

[grizld1]

You should need the choke when starting; if you got cold starts without it, it would mean your pilot mixture was way too fat.

Looks like those air filters didn't come with a reputable kit; they look like the type with thin foam under the screen. If so, I'd advise you to get something better in place. Strip those carbs and check the jetting against the baseline suggested in the VM section of the Carb Guide. Go to the lean side in main jet selection; you'll probably wind up with 175 or 180. Those boots look like OEM BS34 items. If so they're too large for your spigots, and without shrouds and clamps they're going to suck air; don't bother to try to tune those carbs until you have that straightened out. Start from scratch, don't try to take short cuts, and stop trying to second-guess the diagnostics. Don't know what to tell you about those muffs. Get the corks out and see what it sounds like when you get the motor fired.

 

[weekendrider]

Grizld1 caught you while I was typing.
My first thoughts were no intake clamps and check the float level.

 

[gggGary]

Put a good set of stock BS38's and air filters on it. Sell all that stuff to pay for it, let someone else have the tuning headaches.

 

[5twins]

Tuning headaches indeed. Those carbs look like the generic VMs and not a specific kit for your bike. The reason I say that is a kit would come with a right- and left-handed carb while it appears you have 2 lefts. The generic version comes jetted for a two stroke dirt bike so you may need to change every jet and the needles. And those air filters ...... throw one away and use the other on your desk as a pencil holder, that's all it's good for, lol.

 

[grizld1]

One more thought. If those carbs fit snug in the boots they're VM36, not 34; measure the ID of the spigots. If they're VM36, those boots will work with shrouds and clamps in place.

 

[mrkelvinator]

ok so i've gone and adjusted my cam chain tension, valve clearance and contact points. I've pulled one of the carbs apart to clean and these are the numbers that i've found:

- Its a VM36
- Jet needle: 6DP7
- Main jet: 190 (i almost read it as 061 )
- Pilot jet: 22.5
- Needle seat and assembly: 33
- Piston valve: 2.5
- I have yet to find how to check float level...

But are these number ok guys? From what i read in the manual so far the pilot jet and main jet are within range, but im not sure about the jet needle... and whether what i have is good to start out with or should i go n buy something else...

Once again thanks for all the help guys, its greatly appreciated that you share your wisdom with us on these forums

 

[grizld1]

Nope. The needles are 6DP1; you need 6F9. You didn't check the needle jets. The float valve is 3.3, not 33; it'll work. The MJ is probably too rich, but try it. If you had to ask if the jetting was OK, you didn't read the Carb Guide. I'll help you, but I'm not going to rewrite everything I've already written just for you. Any more of that and you're on your own.